One-step template synthesis and solution structures of bis(macrocyclic) octaamine dicopper(II) complexes

Abstract

The template reaction of (1,10-diamino-4,7-diazadecane)copper(II) with formaldehyde, dinitroalkanes (NO2CH2)2(CH2)n(n= 2–4) and base in MeOH yielded 1,n-bis(10-nitro-1,4,8,12-tetraazacyclopentadecyl)alkanes with n= 2, 3 or 4 respectively, co-ordinated to copper(II) in reasonable yields (ca. 30%). The nitro substituents may be reduced with Zn–HCl and the metal-free bis-(pendant amino tetraazamacrocyclic) compounds isolated in ca. 25% yield. The synthesis and spectroscopic properties of the dicopper(II) complexes with nitro substituents and of the bis(pendant amine) metal-free compounds are reported. The similar template reaction of (1,9-diamino-3,7-diazanonane)copper(II) with 1,4-dinitrobutane yielded the corresponding dicopper(II) complex of the bis(14-membered)(CH2)2-linked bis(pendant nitro) bis(macrocyclic) ligand. The dicopper(II) complexes of the bis(pendant nitro) macrocycles do not exhibit any coupling in their EPR spectra irrespective of the size of the bridge. This is in contrast to other dicopper(II) complexes of (CH2)2-linked bis(macrocyclic) ligands. The solution structures of the dicopper(II) complexes of the (CH2)2-linked 14-membered macrocycles and the compound prepared by a similar template reaction with 1,2-diaminoethane instead of 1,4-dinitrobutane were compared using a combination of molecular mechanics calculations and simulation of the EPR spectra. This reveals a stretched conformation for the dicopper(II) complex resulting from the formaldehyde–dinitrobutane template reaction and a face-to-face conformation of that from the formaldehyde–ethylendiamine template reaction.